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Versions: (draft-kiss-simple-winfo-filter-reqs) 00 01

SIMPLE WG                                                        K. Kiss
Internet-Draft                                               E. Leppanen
Expires: July 26, 2004                                      H. Khartabil
                                                                   Nokia
                                                        January 26, 2004


           Requirements for Filtering of Watcher Information
                 draft-ietf-simple-winfo-filter-reqs-01

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on July 26, 2004.

Copyright Notice

   Copyright (C) The Internet Society (2004). All Rights Reserved.

Abstract

   This document defines a set of structured requirements whereby a
   watcher information subscriber (client) may select specific
   information to be received in the watcher information notification
   sent by the notifier (server). The purpose is to limit the content so
   that only essential information is delivered by the server.









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Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.   Conventions  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.   Event Filtering Model  . . . . . . . . . . . . . . . . . . . . 4
   4.   Requirements for Specification of Filters  . . . . . . . . . . 4
   5.   Notification Content Limiting  . . . . . . . . . . . . . . . . 5
   6.   Requirements for Uploading Rules (Operational Rules) . . . . . 5
   7.   Security Considerations  . . . . . . . . . . . . . . . . . . . 6
   8.   Example Applications for Notification Filtering  . . . . . . . 7
   9.   Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
   10.  Changes from previous versions . . . . . . . . . . . . . . . . 7
   10.1 Main changes from version 00 . . . . . . . . . . . . . . . . . 7
        References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 8
        Intellectual Property and Copyright Statements . . . . . . . . 9



































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1. Introduction

   SIP event notification is described in [4]. It defines a general
   framework for subscriptions and notifications for SIP event packages.
   Concrete applications of the general event framework to a specific
   group of events are described in [3] (user presence) and [5] (watcher
   information).

   The watcher information refers to the set of users subscribed to a
   particular resource within a particular event package. Watcher
   information changes dynamically as users subscribe, unsubscribe, are
   approved, or rejected. A client can subscribe to this information.

   As the inherent usage of event packages grows, the client needs some
   mechanisms for controlling the event notifications at the source.
   Evidence of this need is found in [2].

   The Internet Draft describing the watcher information template
   package [5] mentions the possibility for filtering. Accordingly, the
   SUBSCRIBE request may contain a body for filtering the watcher
   information subscription. However, the definition of filtering has
   been left out of the scope of the Internet Draft.

   These mechanisms are expected to be particularly valuable to users of
   wireless devices. The characteristics of these devices typically
   include low bandwidth, low data processing capabilities, small
   display and limited battery power. Such devices can benefit from the
   ability to filter the amount of information generated at the source
   of the event notification.

   However, it is expected that the control mechanisms for event
   notifications add value for all users irrespectively of their device
   or network access characteristics.

   Section 4 and Section 6 of this draft propose a set of requirements
   whereby a client may specify which notifications it is interested in.
   That is, a means to specify filtering rules to be executed by the
   server. Section 8 provides a few example applications of notification
   filtering.

2. Conventions

   In this document, the key words 'MUST', 'MUST NOT', 'REQUIRED',
   'SHALL', 'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY',
   and 'OPTIONAL' are to be interpreted as described in RFC 2119 [1]
   and indicate requirement levels for compliant implementations.





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3. Event Filtering Model

   There are two parts to the event filtering model. From a Watcher
   Information service view point, Watchers subscribe for information
   about a resource. That resource, called watcherinfo subscriber,
   sometimes needs to collect information about the watchers. The first
   part of the model enables the watcherinfo subscriber to limit the
   watcher information delivered to it. Allowing the watcherinfo
   subscriber to select the information of interest to it results in the
   ability to limit the contents of a watcher information document,
   therefore reducing the size of a notification message.


                                                  +--+
                                                --|  |Watcher
    Watcherinfo             Server           ---  +--+
    Subscriber           +---------+     ----
    +-----+              |         |  ---
    |     |              |         |--            +--+
    |     |--------------|         |--------------|  |Watcher
    |     |              |         |--            +--+
    +-----+              |         |  ---
                         +---------+     ----
                                             ---  +--+
                                                --|  |Watcher
                                                  +--+


   The second part of the model defines the triggering. In a filter-less
   subscription, it might be a server's default policy for the first
   NOTIFY after a subscription to carry full state, and subsequent
   notifications to carry partial state. This model enables the
   watcherinfo subscriber to select the events or changes in watcher
   information that trigger notifications to be sent. Other changes in
   watcher state that are not defined as triggers in a filter do not
   result in a notification message being delivered to the watcher.

4. Requirements for Specification of Filters

   The following requirements relate to the creation of filters (rules).

   REQ A1: A common set of constructs MUST be defined for the creation
   of rules. There MUST be a common set of operations that follow a
   common syntax. It MUST be possible for the client to define different
   rules for different purposes using a common filtering mechanism.

   REQ A2: It MUST be possible for the client to indicate the event
   package to which the filter applies.



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   REQ A3: It MUST be possible for the client to indicate the target
   resource  to which a certain filter is applied.

5. Notification Content Limiting

   This chapter presents requirements for specifying the content to be
   sent in the notifications.

   REQ B1: It MUST be possible for the client to specify the XML
   elements in winfo format [6] to be delivered in the notification.

   REQ B2: It MUST be possible to define a set of conditions for the
   values of certain elements in a winfo document that determine which
   elements to send in notifications.

   REQ B3: It MUST be possible to construct expressions that combine
   multiple tests.

   REQ B4: The client MUST be able to instruct the server to include, in
   the notifications, only those watchers that are in a specific state.

   REQ B5: The client MUST be able to indicate to the server to include
   only those watchers in the notifications which are transitioned in
   their current status because of a specific event.

   REQ B6: The client MUST be able to indicate to the server to include
   only those watchers in the notifications which have subscription
   lifetime higher than (less than) a specific amount of seconds.

   REQ B7: The client MUST be able to indicate to the server to include
   only those watchers in the notifications which are subscribed for a
   duration higher than (less than) a specific amount of seconds.

   REQ B8: The client MUST be able to indicate to the server to include
   only certain watchers (e.g. watchers from a particular domain,
   specific watchers defined by the filters) in the notifications.

6. Requirements for Uploading Rules (Operational Rules)

   REQ C1: It MUST be possible for the client to upload the rules to the
   server and know the status - accepted or rejected - based on server
   policy.

   REQ C2: Placing filtering rules in the body of the subscription MUST
   be supported.

   REQ C3: The server MUST retain the uploaded filter setting for the
   duration of the subscription.

   REQ C4: It MUST be possible to change the filter settings during a



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   subscription.

   REQ C5: It MUST be possible for the client to reset the filter
   settings to the service (server) defined default.

   REQ C6 It MUST be possible for a server not supporting filtering  to
   inform the watcherinfo subscriber of the failure.

   REQ C7:  It MUST be possible for a server not understanding a
   filtering  to inform the watcherinfo subscriber of the failure.

   REQ C8: It MUST be possible for a server not accepting a filter to
   inform the watcherinfo subscriber of the reasons for not accepting
   the filter.

   REQ C9: It MUST be possible for the server to terminate a
   subscription if a filter is no longer acceptable, e.g., due to policy
   change or server load.

7. Security Considerations

   Security requirements specified for [3] also applies to winfo
   filtering. Additional security considerations are described as
   follows.

   REQ D1 It SHOULD be possible for the server to hide the fact that a
   filter was not acceptable.

   REQ D2: The presence of a filter in the body in a SIP message has a
   significant effect on the way in which the request is handled at a
   server. As a result, it MUST be possible to authenticate messages
   carrying filters and authorise the watcherinfo subscriber to upload
   filters.

   REQ D3 Modification to filters by an intermediary could also result
   in the watcherinfo subscriber either not receiving notifications of
   watcher information they are interested in or receiving a very large
   watcher info document. Therefore filters SHOULD be integrity
   protected between.

   REQ D4: Processing of requests and looking up filters requires some
   amount of computation. This enables a DoS attack whereby a user can
   send requests with substantial numbers messages with large contents,
   in the hopes of overloading the server. To prevent this the number of
   filters allowed in a request SHOULD be limited.

   REQ D5: Requests containing filters  can reveal sensitive information
   about a UA's capabilities. If this information is sensitive, it



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   SHOULD be encrypted using methods that allow it to be read by those
   nodes that need to do so.

   REQ D6: Authorization SHOULD occur irrespective of the filtering.

8. Example Applications for Notification Filtering

   o  A presentity wishes to see who has subscribed to their presence.
      The presentity only wishes to see information for subscribers who
      are co-workers.

   o  A presentity makes subscription to get information about active
      watchers.

   o  A presentity makes subscription to get information about defined,
      new or unauthorised watchers.

   o  A presentity requests information on watchers that have their
      status as "waiting", for authorization purposes.


9. Acknowledgements

   The authors would like to thank Jonathan Rosenberg, Tim Moran, Juha
   Kalliokulju, Paul Kyzivat and Aki Niemi for their valuable input.

10. Changes from previous versions

10.1 Main changes from version 00

   o  Added filtering model section.

   o  Rephrased some requirements for clarity.

   o  Rearranged requirements into more appropriate sections.

References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [2]  Kiss, K., "Requirements for Presence Service based on 3GPP
        specifications and wireless environment characteristics",
        draft-kiss-simple-presence-wireless-reqs-02, February 2003.

   [3]  Rosenberg, J., "Session Initiation Protocol (SIP) Extensions for
        Presence",  draft-ietf-simple-presence-10.txt, January 2003.




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   [4]  Roach, A., "Session Initiation Protocol (SIP)-Specific Event
        Notification", RFC 3265, June 2002.

   [5]  Rosenberg, J., "A Watcher Information Event Template-Package for
        the Session Initiation Protocol (SIP)",
        draft-ietf-simple-winfo-package-05.txt, January 2003.

   [6]  Rosenberg, J., "An Extensible Markup Language (XML) Based Format
        for Watcher Information",
        draft-ietf-simple-winfo-format-04.txt, January 2003.


Authors' Addresses

   Krisztian Kiss
   Nokia
   P.O. Box 100
   33721 Tampere
   Finland

   Phone: + 358 50 4835363
   EMail: krisztian.kiss@nokia.com


   Eva Leppanen
   Nokia
   P.O BOX 785
   Tampere
   Finland

   Phone: +358 7180 77066
   EMail: eva-maria.leppanen@nokia.com


   Hisham Khartabil
   Nokia
   P.O. Box 321
   Helsinki
   Finland

   Phone: +358 7180 76161
   EMail: hisham.khartabil@nokia.com









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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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